feat(studio): R3 step_respond、运行页 UX 与 R4 思考流式

新增 worldbook 步骤 LLM 回复（thinking/draft/questions/evaluation），
运行页聊天区与产物/选项联动；评价区标签改为「评价与修改建议」；
流式开关开启时 NDJSON 推送思考内容，完成后拆分更新各字段。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/Studio/studioRunUtils.js

@@ -0,0 +1,28 @@
+/**
+ * Resolve bound character display name from workflow variable and/or project meta.
+ */
+export function resolveBoundCharacterName({ boundCharacterVar, characterId, characters = [] }) {
+  if (boundCharacterVar) {
+    const nameMatch = String(boundCharacterVar).match(/名称[：:]\s*(.+?)(?:\n|$)/);
+    if (nameMatch?.[1]?.trim()) {
+      return nameMatch[1].trim();
+    }
+  }
+
+  if (characterId && characters.length > 0) {
+    const byId = characters.find((c) => c.id === characterId);
+    if (byId?.name) return byId.name;
+    const byName = characters.find((c) => c.name === characterId);
+    if (byName?.name) return byName.name;
+  }
+
+  return null;
+}
+
+/** Index of the last user message in stepMessages, or -1. */
+export function findLastUserMessageIndex(stepMessages = []) {
+  for (let i = stepMessages.length - 1; i >= 0; i -= 1) {
+    if (stepMessages[i]?.role === 'user') return i;
+  }
+  return -1;
+}